Triethyl tin (TET) is an organo metal representative of a class of chemicals that produce vacuolization and splitting of myelin. The following research concerned the effects of TET on the developing rat pup. Rats were dosed on postnatal day 5 and neurobehavioral functioning from 21-150 days of age was assessed using neurobehavioral, psychopharmacological, and neurochemical procedures. Postnatal TET appeared to have long lasting effects on behavior and altered the responsiveness of rats of both sexes to apomorphine, a dopamine receptor agonist.